Electrostatic discharge (ESD) is a sudden flow of electricity between electrically charged objects caused by contact, electrical short, dielectric breakdown, and others. If not properly controlled, ESD can damage the objects (e.g., integrated circuits) through which it flows and/or disrupt electrical communication signals.
Certain devices are more susceptible to ESD events due to their design and/or the environment in which they operate. For example, components in a vehicle have no electrical ground and typically operate under high temperature and low humidity, thus creating a favorable environment for electrostatic charges to accumulate. Vehicles' high susceptibility to ESD events, coupled with their increasingly complex and reliance on integrated circuits (e.g., for breaking, accelerating, turning, stability control, cruise control, etc.), make ESD protection particularly crucial in vehicle designs. As an example, the FlexRay communication standard for automobiles, developed by the FlexRay Consortium, includes specific requirements for ESD protection. For instance, inputs/outputs to the bus driver and communication controllers have to withstand voltages of up to +/−60V and pass a 6 kV HMM (Human Metal Model) ESD stress test.
A transceiver under the FlexRay standard, for example, communicates information using two differential signal lines, Bus Plus (BP) and Bus Minus (BM). More specifically, whether a bit is 0 or 1 depends on whether BP−BM is negative or positive. To protect BP and BM from ESD events, it is conventional to use three ESD protection devices, each of which has two nodes. A typical configuration places a first ESD protection device between BP and Vss (negative supply voltage), a second ESD protection device between BM and Vss, and a third ESD protection device between BP and BM. The three dual-node ESD protection devices take up considerable real estate on a substrate, which in undesirable.